Expandable reamers are typically employed for enlarging subterranean boreholes. In drilling oil, gas, and geothermal wells, casing is installed and cemented to prevent the wellbore walls from caving into the subterranean borehole while also providing requisite shoring for subsequent drilling operation to achieve greater depths. Casing is also conventionally installed to mutually isolate different formations, to prevent crossflow of formation fluids, and to enable control of formation fluids and pressure as the borehole is being drilled. To increase the depth of a previously drilled borehole, new and smaller diameter casing, or “liner,” is disposed within and extended below the previous casing. However, while adding additional casing allows a borehole to reach greater depths, the additional, smaller casing has the disadvantage of narrowing the borehole. Narrowing the borehole restricts the diameter of any subsequent sections of the well because the drill bit and any further casing must pass through the smaller casing. As reductions in the borehole diameter are undesirable because they limit the production flow rate of oil and gas through the borehole, it is often desirable to enlarge a subterranean borehole to provide a larger borehole diameter beyond previously installed casing to enable better production flow rates of hydrocarbons through the borehole.
Various approaches to expand a borehole may include expandable stabilizer blocks or bearing pads used in an expandable stabilizer located longitudinally above an expandable reamer to increase stability and reduce dysfunctional loads, i.e., lateral vibrational loads, thereupon while reaming. In most instances, fixed stabilizer pads or blocks, being sized and configured for a corresponding hole diameter cut by a pilot bit or drill bit, are located in a drill string between the bit and the expandable reamer. The stabilizer bearing pads or blocks help to control stability, particularly when conducting a so called “down drill” operation, e.g., drilling in the down-hole direction. Also, stability is further improved by providing a point of control above an expandable reamer to decrease the flexibility of the drill string about the expandable reamer.